I. Field of the Invention
The present invention relates to the field of electric arc welding in which a steady supply of welding wire is supplied to a contact electrode of an arc welding apparatus. More specifically, the invention relates to an apparatus for rapidly shutting off the electric power supplied to the welding contact electrode when the steady supply of welding wire is interrupted. The invention further concerns apparatus for sensing when the supply of welding wire is interrupted.
II. Prior Art and Other Considerations
In electric welding operations where a welding wire is supplied from a coil to welding contact electrode, a serious condition results when the supply of wire to the electrode is interrupted while the electrode is still receiving electric power. The electrode can be damaged from excessive heat when the wire is not present at the electrode unless the power to the electrode is turned off promptly.
There are basically three types of circumstances in which the steady supply of wire to the electrode is interrupted. In the first case, the wire on the supply coil or spool is simply exhausted. In the second case, the welding wire suffers a break between the supply coil and welding electrode. In the third case, a tangle or knot present in a spool of welding wire causes the supply of wire to the electrode to be interrupted.
In the prior art, several approaches have been proposed to solve some of the problems involved in the interruption of the steady supply of welding wire. In this regard, U.S. Pat. No. 3,268,709 to Olds discloses a control apparatus for interrupting electric power to an electric arc welder. The Olds device is comprised of a spring-biased plunger which moves in two opposite directions on a guide formed on two opposing inside walls of a housing. The plunger contacts one of two separate switches placed on opposing housing walls at opposite ends of the plunger. A first switch senses the absence of wire being fed to the control apparatus. A second switch senses a tangle in the wire being fed from the coil. The spring-loaded plunger is biased in a first direction, and the plunger moves in the direction of the spring bias in response to the condition of no wire being present at the plunger. The plunger receives the moving wire upon a grooved roller connected to the plunger, and the roller serves to guide the wire out of the control apparatus. A second grooved roller is placed on the control apparatus housing at the entrance of the wire to the apparatus. The roller on the housing and the roller on the plunger cooperate to guide the wire through the control apparatus when the wire moves freely without being tangled. When the wire is tangled, the force of the wire overcomes the biasing force and forces the plunger to the second direction to contact the second switch.
The Olds patent shows a cumbersome and complex device employing a plurality of rollers and a plurality of switches. In addition, in prior art devices such as those depicted by the Olds patent a tangled wire might temporarily turn off the signal to the welding arc, but there is no assurance that the signal would remain turned off until the tangle is rectified. Moreover, in a device such as Olds, a roll of wire having considerable slack would improperly cause the plunger to depress a switch and thereby needlessly turn off the power supply to the welding arc.
Accordingly, it is an object of the present invention to provide a simple apparatus that mechanically monitors the wire fed to an electric arc welding apparatus.
Another advantage of the present invention is the provision of a relatively simple wire monitoring apparatus which obviates the need of complex mechanical and electrical structure.